The major objective of this project is to characterize the mechanisms of inactivation for norepinephrine (NE) in vascular tissue. The experiments will be performed on rabbit aorta because the neuronal and extraneuronal components of inactivation can be physically separated in this tissue by stripping the adventitia off of the media. To study the neuronal and extraneuronal transport systems, the tissue will be pretreated with inhibitors of monoamine oxidase, catechol-O-methyl transferase and granular uptake so that NE is not removed from the cytoplasm after it is transported into the cell. Several experiments will be performed to determine that these pretreatments do not directly affect the transport systems. The kinetics of uptake and efflux of NE and several of its analogs will be examined. The effect of several drugs, inorganic ions and metabolic inhibitors on NE uptake and efflux will also be determined. From these experiments, an attempt will be made to determine whether the mechanism of transport is passive diffusion, facilitated diffusion, or co-transport. The properties of monoamine oxidase and catechol-O-methyl transferase will be studied in homogenates of the isolated adventitia and media. The following characteristics of these enzymes will be determined: subcellular distribution, substrate specificity, and sensitivity of inhibitors.